Bully for them! This is so much better than an in store protest. Would have been even better if they hadn’t backed it with an on-line petition.
That being said, I agree with your assessment, Mr. Cathy should very politely decline.
I agree.I'd send a letter saying "on the advice of my physician,I'm at increased risk of infection due to ongoing chemotherapy and,therefore should not risk contracting any of the exotic infections to which I might be exposed in your home".